Fig. 2.

Chemical modifications of oligonucleotides. Chemical structure of a GC dinucleotide is shown (blue box) in which R = H for DNA and R = OH for RNA; PO = phosphodiester and PS = phosphorothioate. Examples of heterocyclic nucleobase (light green box) and sugar (light salmon box) modifications are shown. Two examples of sugar-phosphodiester backbone modifications are also presented (light gray box). Abbreviations: 2′-O-Me, 2′-O-methyl; 2′-O-MOE, 2′-O-methoxyethyl; B, heterocyclic nucleobase; 5-mehtyl C, 5-methylcytosine; LNA, locked nucleic acid; PNA, peptide nucleic acid and PMO, phosphorodiamidate morpholino oligomers